To generate white light in what are known as LARP (laser activated remote phosphor) systems which have a phosphor that emits in the yellow wavelength range, blue light must be added to the converted yellow light. The component of the blue light is critical for the color locus of the total luminous flux. Radiation whose spectrum is in the blue wavelength range is typically used as the excitation radiation.
In conventional LARP systems, which use a phosphor wheel, a blue channel is created via a slot in the phosphor wheel, and the blue excitation radiation is added to the converted light. The slot in the phosphor wheel is fixed in terms of size and position, and the blue component in the white light can be changed to a specific degree only by a pulsed current change of the laser diodes which are used for generating the excitation radiation. In other words, the output in the blue region of the phosphor wheel, i.e. in that region where the slot is arranged, can be maximized as compared to the operation with nominal power in that region of the phosphor wheel in which the phosphor emitting in the yellow wavelength range is arranged. However, operation with high output, above the nominal power, reduces the lifetime of the laser diodes. Yet increasing the size of the blue segment, i.e. the slot, leaves less segment region for the remaining coloration such that a larger tunable region comes at a price of a considerable loss in total luminous flux.